Telephone system



Dec. 30, 1941. T. F. cRocKER TELEPHONE SYSTEM Filed June 8, 1940 9 sheets-sneer 1 INVENTOR THOMAS F. cRocKER IM ,vx/L@ AUORNEYS Dec. 30, 1941. T F. CRQCKER 2,268,019

TELEPHONE SYSTEM Filed June 8, 1940 9 Sheets-Sheet 3 @Wea/N6 TR1/Nif UNE c/RcU/T E @360 N L: 200 305 ,5,206 32h13 `;3/\| +/NCO/w//V6 /?1//v/fL//vc/Rc1//300..

332/ L 535/, j 205 WW -4 ff 34/ ma* 350 c5527 f C207 P322 C353) j I [6M T/@UNK UNE c/Roz//T 400 1 450 646/7 Dec. 30, 1941. T F, CRQCKER 2,268,019

, TELEPHONE SYSTEM ATTORNEYS T. F. CROCKER TELEPHONE SYSTEM Dec. 30, 1941. 2,268,019

Fi1-ed June 8, 1940 9 Shee'ts--Sheet 5 Dec. 30, 1941.

F/NDER 700 can a/g T. F. CROCKER TELEPHONE SYSTEM Filed June 8. 1940 sw L//wf 800 SELECTOR 820 9 Sheets-Sheet 6 INVENTOR THWAS E CROGKER BY. y

TTORNEYS 9 shams-sheet '7 Filed June 8, 1940 INVENTOR THOMAS F. CROGKER Dec. 30, 1941. l r F, CROCKER 2,268,019

TELEPHONE SYSTEM Filed June 8, 1940 9 Sheets-Sheet B.

,09, ,092 Asr Pos/r/o/v APPARATUS /000 Fi .1U /asn Aoi-@ A056. i J L INVENTOR THOMAS F. CROCKER ATTORNEYS Dec. 30,1941. T CR'OCKER 2,268,019

TELEPHONE SYSTEM C675z f//7/ c3562 L//49 Tfl/ 74 ATTORNEYS Patented Dec. 30, 1941 UNITED STATES PATENT OFFICE elated Electric Laboratories, Inc., Chicago, Ill a corporation of Delaware Application June 8, 1940, Serial No. 339,431

13 Claims.

The present invention relates to telephone systems and more particularly to improved automatic switching apparatus of the character of that disclosed and claimed in U. S. Patent No. 2,070,874, John H. Voss and Thomas F. Crocker, issued February 16, 1937, which apparatus is connected and arranged to handle switchboard traiiic.

It is the principal object of the present invention to provide, at an operator switchboard position in a telephone system, improved position equipment of the character of that disclosed and claimed in the copending application of Smart S. McAndrew, Serial No. 339,475, led June 8, 1940, in order to facilitate the answering of calls and the extension and supervision of established connections at the operator switchboard position in a ready and velicient manner.

A further and more specic object of the invention is to provide, at a number of operator switchboard positions in a telephone system, improved position equipment which is so connected and arranged that automatic switches individually associated with the operator switchboard positions may be selectively controlled to select lines distant exchange of any suitable type. A switch-- board is arranged in the P. A. B. X which comprises a number of operator positions. Further a tol switch train is arranged in the P. A. B. X which comprises a number of groups of switching links individually associated with the operator positions, each switching link including an answer switch and a call switch, the answer switch and the call switch of each switching link having access to trunk lines and toll lines interconnecting the central otllce, the I. B. X and the distant exchange with the P. A. B. X.

In accordance with one feature of the invention, the telephone system comprises a plurality of lines, a plurality of operator positions, a plurality of automatic switches individually associated with the operator positions and having access tothe lines, normally effective means selectively controllable from each of the operator positions for causing the associated switch to operate and select any particular one of the lines nl un and means controlled while one of the switches is operating to select a given line for restricting the operation of each of the other of the switches, whereby each of the other of the switches is operative to select any particular one of the lines excepting the given line while the one switch is operating to select the given line.

In accordance with another feature of the invention, the system comprises a plurality of vdevices at each of the operator positions individually corresponding to the lines, the devices at the operator positions corresponding to the same line constituting a group, a plurality of relays individually associated with the devices, the relays associated with the same group of devices constituting a group, means responsive to the rst device operated in -any given group of devices for causing operation of the associated relay in the associated group of relays and for preventing operation of the remainderof the relays in the associated group of relays, and means responsive to the operation of any given relay in any given group of relays for'c'ausing the associated switch to operate and select the corresponding line, thereby to complete a connection between the associated operator position and the last-mentioned line. More particularly, any given relay in any given group of relays is operative to-mark the corresponding line and to initiate operation of the associated switch, means being provided which is controlled when one of the switches selects a marked line for arresting operationpf the switch. More specifically, the relays are of the marginal type and are so'connected and arranged that, when any given relay in anyr given group of relays is energized, it completes a locking circuit for itself which prevents adequate energization of the remainder of the relays in the given group of relays and consequently operation of the remainder of the relays in the given group of relays.

Further features of the invention pertain to the- Descriptonrof the apparatus incorporated in the telephone system Referring now more particularly to Fig. 1 of the drawings the telephone system there illustrated comprises a central oilice 20, a P. A. B. X 30, an I. B. X 40 and a distant exchange 50. The central ofilce 20 and the distant exchange 50 are of any well-known type, each serving a 'number of subscriber substations not shown; while the P. A. B. X 30 and the I. B. X 40 `are of the automatic type, each serving a number of automatic subscriber substations. More particularly, the P. A. B. X 30 serves a number of subscriber substations, including the subscriber substations T3 and T4; while the I. B. X 40 serves a number of subscriber substations, including the subscriber substations TI and T2. The central ofce and the P. A. B. X 30 are interconnected by a group of one-way trunk lines, including the trunk line 205, extending from the central omce 20'to the P. A. B. X 30, and a group of one-way trunk lines, including the trunk line 200, extending from the P. A. B. X 30 to the central oiilce 20. The I. B. X 40 and the P. A. B. X 30 are interconnected by a group of two-way trunk lines, including the trunk line 2|0, extendingV therebetween; while the distant exchange 50 and the P. A. B. X 30 are interconnected by a group of two-way toll lines, including the toll line 2|5,.-extending therebetween.

The central ofiice, 20 the I. B. X 40 and the distant exchange 50 respectively comprise an operator position 240, an operator position .260, and a toll operator position 250; while the P. A. B. X 30 comprises an automatic dial switchboard provided with a number of operator positions, including a first operator position 900 and a last operator position 9| 0. Each trunk line in the group of trunk lines extending from the central oice 20 to the P. A. B. X 30 terminates at th'e operator position 240 in the central oiiice 20 and in an incoming trunk line circuit in the P. A. B. X 30, the trunk line 205 terminating at the operator position 240 and in the incoming trunk line circuit 300. Similarly, each trunk line `in the group of trunk linesextendng from the P. A. B. X 30 to the central oflice 20 terminates in an outgoing trunk line circuit in the P.A. B. X 30 and at the operator position 240 in the central oillce 20, the trunk line 200 terminating in the outgoing trunk line circuit 360 and at the operator position 240. Also, eachl trunk r1line in the group of trunk lines extending between the I. B. X 40 and the P. A. B. X 30 terminates in a.trunk line circuit in the P. A. B. X 30, and at the operator position 260 in the I. B. X 40, the trunk line 2|0 terminating in the trunk line circuit 400 and at the operator position 260. Finally, each toll line in the group of toll lines extending between the distant exchange 50 `andthe P. A. B. X30 terminates atthe operator position 250 in thedistant exchange 5 0 and in a toll line circuit in th'e P. A. B. X 30, the toll line 2I5 terminating at the operatorposition 250 and in the toll line circuit 500.

The I. B. X 40.is provided with aswitch train comprising a number of under-connector links, including the under-connector link 230. Also, a telephone line havinga line circuit individually associated therewith extends to each of the subscriber substations in the I. B. X 40, the telephone lines 220 and 225 respectively extending to the subscriber substationsTI and'I2 and having the line circuits 22| and 226 respectively associated therewith. Finally, a number of trunk circuits are provided in the I. B. X 40 which are individually associated with trunks terminating at the operator position 260 in the I. B. "X 40, the trunk circuit 236 being individually associated with the trunk 235 terminating at th'e opera-tor position 260. It is noted that each finder-connector link in the I. B. X 40 has access to each telephone line therein and to each trunk terminating at th'e operator position 260.

The P. A. B. X 30 is provided with a local switch train comprising a number of local finder-selector links, including the local finder-selector link 940, and a number of local connectors, including the local connector 94|. Also, teleph'one lines' having linevcircuits individually associated therewith extend'to each subscriber substation inthe P. A. B. X 30, the telephone lines 930 and 935 respectivelyvextending to the subscriber substations T3 and T4 and having the line circuits 93| and 936 respectively associated therewith. A number of trunkclrcuits, including the trunk circuit 600, is provided in the P. A. B. X 30. It is noted that each of the local nder-selector links h'as access to each telephone line in the P. A. B. X 30, to each local connector and to a number of trunks individually extending to the trunk circuits, the trunk 680 individually extending to the trunk circuit 600.

Further the P. A. B. X 30 is provided with a toll switch train comprising a number of groups of switching links individually associated with the operator positions, one of the groups, including the switching links 800 and 902, being individually associated with' the ilrst operator position 900, and another of the groups, including the switching links 9|2 and 9|6, being individually associated with the last operator position 9 0. Each of the switching links comprises a finder and a selector, the switching links 800, 902,9l2and9l6respectively, comprising the finders 100, 903, 9|3and 9|`| and the selectors 820, 904, 9|4 and 9|8. Also it is noted that each of the switching links in the group, includingl the switching links 800 and 902, is commonly associated with a cable extending to the rst operator position 900; while each of the switching links in the group, including the switching links 9|2 and 9|6, is commonly associated with a cable 9|| 'extending to the last operator position 9|0.

It is noted that each of the finders has access to a group of trunks individually extending to the group of outgoing trunk line circuits, this group including the ltrunk 305 extending to the outgoing trunk line circuit 360; to a group of trunks individually extending to the group of incoming trunk line circuits, this group including the trunk 350 extending to the incoming trunk line circuit 300; to a group 'of trunks individually extending to the group of trunk line circuits, this. groupincluding the trunk 460 extending to the trunk line circuit 400; to a group'of trunks individually" extending to the group of toll line circuits, this group including the trunk 590 extending to the toll line circuit 600; and to a group of trunks individually extendingto the group of trunk circuits', this group including thetrunk 610 extending to the trunk circuit 600.k Similarly, each of the selectors has access to the group of .trunks individually extending to the group of outgoing trunk line circuits, this group including the trunk 305 extending to the outgoing trunk line circuit 360; to the group of trunksindividually extending to the group of trunk line circuits, this group including the trunk 460 extending to the trunk line circuit 400; to the group oi' trunks individually extending to the group of toll line circuits, this group including the trunk 590 extending to the toll line circuit 500; and to a group of trunks individually extending to the local connectors in the local switch train, this group lncluding the trunk 945 extending to the local connector 94|.

Each operator position at the switchboard in the P. A. B. X 30 comprises position equipment including position apparatus, the position equipment provided at the iirst operator position 900 and at the last operator position 9|0 respectively including the ,first position apparatus H and the last position apparatus |000. l

The operator position 240 in the central oiilee 20. as best shown in Fig. 2, the operator position 260 in the I. B. X 40, as best shown in Fig. 2, and the toll operator position 250 in the distant exchange 50, as best shown in Fig. 2,'are connected and arranged in a conventional manner. Also the subscriber substations TI and T2 in the I. B. X 40, as best shown in Fig. 2, comprise conventional substation equipment; while the line circuits and trunk circuits respectively associated with the telephone lines and the trunks in the I. B. X 40, as best shown in Fig. 2, are connected and arranged in a conventional manner. Further the finder-connector links in the switch train in the I. B. X 40, as best shown in Fig. 2, are connected and arranged in a conventional manner; preferably, each of. these links comprising a iinder -and a connector of the well-known Strowger type.

Preferably, each of the outgoing trunk line circuits is identical to the outgoing trunk line circuit 360, shown in Fig. 3; which is connected and arranged in a conventional manner; while each of the incoming trunk line circuits is identical to the incoming trunk line circuit 300, shown in Fig. 3. The incoming trunk line circuit 300 comprises a repeater 340 and a number of relays, including a ring-up relay R3I0, a start relay R320 and a cutoif relay R330, connected and arranged in a. manner more fully described subsequently.

Preferably, each of the trunk line circuits is identical to the trunk line circuit 400, shown in Fig. 4, which comprises a repeater 450 and a number of relays, including a control relay R4I0,

a start relay R420, a cutoi relay R430 and a line relay R440, connected and arranged in a manner more fully described subsequently.

Preferably, each of the toll line circuits is identical to the toll line circuit 500, shown in Fig. 5, which comprises a repeater 50i and a number of relays, including a ring-off relay. R5I0, a start relay R520, two control relays R530 and- R560, acutoff relay R540, a.' ringp relay R550, a guard relay R565, a timer relay R510, a hold relay R515 and two count relays R500 and R585, connected and arranged in a manner more fully described subsequently.

Preferably, each of the trunk circuits is identical to the trunk circuit 600, shown in-Fig. 6, which comprises a repeater 660 and a number of relays, including a cutoi relay R6|0,` a, start relay R620, a, line relay R630, a hold relay R640 and a recall conventional substation equipment; while the line circuits associated with the telephone lines in the P. A. B. X 30, as best shown in Fig. 9, are con- `nected and arranged in a conventional manner.

Further the local finder-selector links and the local connectors in the local switch train in the P. A. B. .X 30, as best shown in Fig. 9. are connected and arranged in a conventional manner; preferably, each of the localnder-selector links comprising a local nder and a local selector, the local nders, the local selectors and the local connectors being of the well-known Strowger type.

Preferably, each of the switching links 800, 902, 9I2, 9I6, etc., shown in Figs. 7, 8 and 9, are identical, each of these switching links comprising a finder and a selector. ,The nder of each switching link, such as the finder 100, shown in Figs.' 7

and 8, of the switching link 800, is connected andy arranged in a manner substantially identical to that of the finder shown in Fig. 7, part 1 and Fig. "I, part 2 of the previously mentioned Voss and Crocker patent; while the selector of each switching link, such as the selector 820, shown in Fig. 8,

of the switching link 800, is connected and arranged in a manner substantially identical to that of the selector shown in Fig. 8 of the previously mentioned Voss and Crocker patent. More particularly, the finder 100 comprises a switching mechanism 1I0 of the Strowger type, including a main wiper set provided with a number of wipers 1H to 1|6, inclusive, and capable of both vertical and rotary movements, and an associated main contact bank, including ten vertical levels of contact sets arranged in circumferentially spaced-apart relationship. Also the mech-- anism 1|0 includes'a vertical control wiper 1| 1, capable of. vertical movement, and an associated vertical control contact bank'1l0. The mechanism 1 I 0 is provided with a vertical magnet M110 for moving the wiper set thereof in the vertical direction, a rotary magnet M120 for moving the wiper set Athereof in the rotary direction and a release magnet M122 for releasing the wiper set thereof and for causing the wiper set thereof to be returned to its normal position. Finally the switching mechanism 1l0 has a number of sets of switch springs S123 and S124 operatively associated therewith, which are controlled in accordance with the movements of the wiper set thereof, in a manner more fully described subsequently.

Further the nderf100 comprises a group of relays, including a switching relay R130, a transfer relay R140, a step relay R150, a start relay R155, a test relay R160v and a connect relay R110, connected and arranged in a manner more fully described subsequently. Moreover, the iinder 100 relay R650, connected and arranged in a manner more fully described subsequently.

The subscriber substations T3 and T4 in the y has individually associated therewith a link listening or talk key K180 and a monitor key, not shown. which are operative to associate the nder with the cable 90| extending to the rst operator position 900. Finally, a number of supervisory lamps L and L126 are associated with the finder 100 for supervisory purposes.

Each operator the P. A. B. X 30, such as the rst operator position 900 and the last operator position 9l0,shown in Fig. 9, comprises position equipment including a trunk circuit, a telephone instrument, key sender apparatus, a number of control keys operlative selectively to render different types of services over connections established at theoperator position, and position apparatus. More particuposition at the switchboard inv and the control keys in the position equipment at each operator position are connected and arranged in the manner of the trunk circuit, telephone instrument and control keys in the.posi tion equipment, shown in Fig. 21, part 1, Fig. 21, part 2 and Fig. 21, part 3, of the previously mentioned Voss and Crocker patent; while the key sender apparatus in the position equipment at each operator position is connected and arranged in the manner of the key sender apparatus in 'and K||65, a number of group line supervisory lamps, including the group line supervisory lamps L||48 and L||49, a number of individual line answer lamps, including the individual line answer lamps LI |41 and LI |45, and a number of individual line busy lamps, including the individual line busy lamps L|`|46 and LI |44. Also, the rst position apparatus comprises a number of lockout relays, including the lockout relays RI |25 and R||30, individually associated with the individual line keys, the locking relays RI |25 and RI |30 being respectively individually associated with the'individual line keys K||65 and KI |60. i

Similarly, the last position apparatus |000 in the position equipment at the lastoperator position 9|0 comprises, as best shown in Fig. 10, a number of group line keys, including the group line keys K|050 and K|055, a number of individual line keys, including the individual line keys K|060 and K|065, a number of group line supervisory lamps, including the group line supervisory lamps L|048 and Ll049, a number of individual line answer lamps, including the individual line answer lamps LI 041 and L|045, and a number of individual line busy lamps, including theindividual line busy lamps L|046 and L|044. Also, the last position apparatus|000 comprises a number of lockout relays, including the lockout 'relays R|025 and VR|030, individually associated with the individual line keys, the locking relays R|025 and R|030 being respectively individually associated with the individual line keys K|065 and KI 060.

Further., it is noted that a number of line marking relays including the line marking relays RI |10 and RI |80 are co'mmonly associated with the individual line keys in both the first position apparatus ||00 and the last position apparatus |000 in a manner more fully explained subsequently. Further, in connection with the last position apparatus |000 and the iirst position apparatus H00, it is noted that the group line keys K|050 and KI |50 commonly correspond to the group of incoming trunk line circuits, including the incoming trunk line circuit 300; while the group line keys K|055 and KI commonly correspond to the group of trunkcircuits, including the trunk circuit 600. Similarly, in the last position apparatus |000 and the first position apparatus ||00 the individual line keys K|l060 and Kl commonly correspond to the individual toll line cir- I- cuit 500 in the associated group of toll line circuits; while the individual line keys K|065 and K|| commonly correspond to the individual trunk line circuit 400 in the associated group of trunk line circuits.

More particularly, it is noted that the individual line keys which correspond to the same circuit constitute a group. For example, the individual line keys K|065, KI |65, etc., constitute a group, while the individual line keys K|060, KI |60, etc., constitute a group. Also, thelockout relays which are associated with the individual line keys in a given group of individual line keys constitute a group. For example, the lockout relays R|025. RI |25, etc., respectively individually associated with the individual line keys K|065, Kl |65, etc., in this group of individual line'keys, constitute a group; while the lockout relays Rl030, RI |30, etc., respectively individually associated with the individual line keys.K|060, K||60, etc., in this group of individual line keys, constitute a group. Further, it is noted that each group oi' lockout relays has a line marking relay individually associated therewith, the group of lockout relays including the lockout relays R|025, RI |25, etc., having the line marking relay Rl |10 individually associated therewith and the group of lockout relays including the lockout relays R|030, R| |30,

etc., having the line marking relay R|I inl Local call from a subscriber substation yin the P. A. B. X to the switchboard in the P. A. B. X

In order to extend a call Vfrom a subscriber substation, such as the subscriber substation T4 in the P. A. B. X 30 to the switchboard therein, a call operation is ilrst performed at the calling subscriber substation T4, thereby to cause the line circuit 936 individually associated with the telephone line 935 extending to the subscriber substation T4 to operate. Upon operating, the line circuit 936 initiates operation oi one of the local finder-selector links, such as the local nder-selector link 940 in the local switch train, whereupon the local lnder-selector link 940 operates to seize the telephone line 935 extending to the calling subscriber substation T4. When the local finder-selector link 940 seizes the telephone line 935 extending to the calling subscriber substation T4, the line circuit 936 operates to mark the telephone line 935 as busy to the local connectors having access thereto and the local iinder-selector link 940 is rendered responsive to a digit dialed thereinto. The subscriber at the subscriber substation T4 then dials a predetermined digit thereat, thereby to cause the local flnderselector link 940 to operate and select an idle trunk in the associated group of trunks extending to the group of trunk circuits. Assuming that the local finder-selector link 940 operates to seize the trunk 680 extending to the trunk circuit 600, when the trunk 680 is thus seized a circuit is completed for energizing in series the upper and lower windings of the line relay R630 in the trunk circuit 600, vthis circuit extending from ground by way of the lower winding of R630 and the winding 662 ofthe repeater 660 to the line conductor C682 of the trunk 680, and from battery 2,268,019 line conductors C68| and C662 of the trunk 680 extinguished condition of the supervisory lamp being connected by way of the local iindeij-selec- L125. When the talk key K180 oi' the iinder 100 tor link 940 to the telephone line 936. Accordoi' the switching link 800 is operated away from ingly, at this time, an operative connection is completed between the calling subscriber substation T4 and the repeater 660.

When thus energized the line relay R630 operates to complete, at the contacts 63|, an obvious path for returning ring-back tone current over the trunk 680, the local iinder-selector link '940 and the telephone line 935 to the calling subscriber substation T4, thereby to simulate at the T4 tential by way ofthe v conductor C683 thereof. Finally R646 completes, at the contacts circuit for energizing the control the hold relay 645, an obvious of the trunk 610, to mark the rotary position of the trunk 610 in the main contact banks of the switching mecha-- having access thereto. Fur- R620 completes, at the contacts 625, an obvious path for applying ground potential to the control conductor C615, the control conductor C615 being commonly associated to the operators thereat that there is a call waiting to be answered on a trunk in the group of trunks including the trunk' 610.

The call on the trunk example, ing link 800 is selected by the operator at the rst operator position 900 at this time, this switching link is indicated as being idle by the at the contacts 642 its normal position there contacts 18| thereof, a circuit for energizing the the conductors 802 and 803 extending by Way of to the selector ltion 900 operates kfrom its normal position there is completed, at the the finder 100 of the switching link lll is in readiness to be operated in order to route a call to the first operator position 900.

When the operator at the first operator posithe group line key KI |55 away contacts H51 thereof, an obvious path for applying ground potential to the marking conductor C|016 in the cable |090. 'Ihis application of ground potential to the marking conductor C1019 in the cable |090 marks the vertical level in the vertical control contact banks; of the switching mechanisms of the finders of the switching links, wherein the trunk 610 extending to the trunk cir- 'cuit 800 is terminated. Also, at the contacts H56 of the group line key Ki |55, there is completed an obvious path for applying ground potential to the start conductor C|018 in the cable |09| extending to the first operator position 900, which ground potential is forwarded by way of the position equipment at the first operator position 900 to the start conductor C 010 in the cable 90|. This application of ground potential to the start conductor C|018 in the cable 90| completes the previously mentioned circuit for energizing the upper winding of the start relay R155, this circuit extending from the grounded start conductor C|018 in the cable 90| by way of the contacts 112', the set of switch springs S124 and the upper winding of R155 to battery. When I thus energized the start relay R155 operates to complete, at the contacts 155, an obvious point in multiple with the set of switch springs S124 in the previously traced circuit for energizing the lupper winding tacts 158, an obvious circuit for illuminating the supervisory lamp L125, thereby to indicate to the operator at the first operator position 9,00 that the switching link 800 is busy at this time. `Also the start relay R155 completes, at the contacts 151, an obvious holding circuit forenergizing the lower winding of the switching relay R130, thereby to render the switching relay R130 exceed- .ngly fast to operate when the upper winding '.hereof is energized, the switching relay R130 beng of the polarized type. Further the start relay t155 completes, at the contacts 151, a circuit for energizing the vertical magnet M1 I8, this circuit extending from ground by way of the contacts |51, 131, 152 and 145 and the vertical magnet M1|8 to battery. When thus energized the verti- :al magnet M1|8 operates to drive the wiper set )f the switching mechanism rertical direction and to complete, at the con- :acts 1|9, an obvious circuit for energizing the winding of the step relay R150, thereby to cause the latter relay to operate. Upon operating, the step relay R150 interrupts, at the contacts 152, the previously traced circuit for energizing the vertical magnet M1|8 and prepares, at the contacts a test circuit traced hereinafter for energizing the lower winding of the transfer relay R140. The vertical magnet M1|8 then restores to interrupt, at the contacts 1|9, the previously mentioned circuit for energizing the winding of the step relay R150, thereby to cause the latter 'relay to restore. Upon restoring, the step relay R150 interrupts, atthe contacts 15|, a point in the previously mentioned test circuit for energizing the lower winding of the transfer relay R140 and recompletes, at the contacts 152, the previously traced circuit for energizing the vertical magnet M1 I8. Accordingly, the vertical magnet M1 |8 and the step relay R150 interact in the manner described above, thereby to thereof, to complete, at the con- I 1|0 one step in the of the vertical control wiper 1 I1 and v the step relay R150, thereby to cause the wiper set of the mechanism 1|0 to be driven step by step inthe vertical direction until the vertical control wiper 1|1 engages a contact in the associated vertical control-contact bank 1|8 having ground potential thereon.

In thepresent example, the vertical magnet M1|8 is energized intermittently six times, whereupon the vertical control wiper 1 I1 engages the contact in' the associated vertical control contact bank 1|8 terminating the marking conductor C|010 having ground potential thereon, whereupon the previously mentioned test circuit for energizing the lower winding of the transfer relay R140 iscompleted. This circuit extends from the groundedmarking conductor C|015 by way engaged contact in the associatedvertical'control contact bank 1|8, the contacts 143, the lower winding of R140, the contacts -15| and 145 and the vertical magnet M1|0 to battery. When this series circuit is completed the vertical magnet M1|8 remains in its operated position, thereby to retain the step vrelay R150 in its operated position and the transfer relay R140 is operated shortly thereafter, the transfer relay R140 being of the slowto-operate type. Upon operating, the transfer relay R140 completes, at the contacts 142, a holding circuit for energizing the upper winding thereof, this circuit extending from ground by way of the contacts 151, 131 and 142 and the upper winding of R140 to battery. Further the transfer relayR140 interrupts, at the contacts 143, the previously traced series circuit for energizing the lower winding of the .transfer relay R140 and the vertical magnet M1|8, thereby to cause the vertical magnet M1|8 to restore. Finally, the transfer relay R140 interrupts, at the contacts x145, a furtherv point in the previously tracedy circuitfor energizing the vertical magnet M1|8 and prepares, at the contacts 144, a circuit traced hereinafter for energizing the M120. Upon restoring, the verinterrupts, at the contacts 1 |9, the previously mentioned circuit for energizing the winding of the step relay R150, thereby to cause the latter relay to restore.

Upon restoring,`the step relay R150 interrupts, at the contacts 15|, a further point in the previously traced series circuit for energizing the lower winding of the transfer relay R140 and the vertical magnet M1|8 and completes, at the contacts 152, the previously mentioned circuit for energizing'the rotary magnet M120. This circuit extends from ground by way of the contacts 151, 131, 152 and 144 and the rotary magnet M120 to battery. When thus energized the rotary magnet M120 operates to drive the wiper set of the switching mechanism 1|0 one step in the rotary direction and to complete, at the contacts 12|, an obvious circuit for energizing the winding of cause the latter relay to operate. Upon operating, the step relay R150 interrupts, at the contacts 152, the previously traced circuit for energizing the rotary magnet M120, thereby to cause the rotary magnet M120 to restore. Accordingly, the rotary magnet `M120 and the step relay R150 interact; yin the thereby to cause the mechanism 1|0 tobe extends from ground by way of the contacts 151,

the upper winding of R136, the contacts 162, the control wiper 1I3 of the switching mechanism 1I0, the control conductor C613 of the trunk 610, the contacts 622 and the upper winding of R6|0 to battery. When this series circuit is completed the switching relay R130 operates exceedingly fast, thereby to interrupt, at the contacts 131, a further point in the previously traced circuit for energizing the rotary magnet M120 in order positively to prevent further opera-tion of the switching mechanism 1|0. Also the switching relay R130 completes, at the contacts 135, a holding circuit for energizing the intermediate winding thereof, this circuit extending from groundby way of lthe contacts 151 and 135 and the intermediate winding of R130 to battery. Further theswitching relay R130 completes, at the contacts 136, an obvious path for short-circuiting the upper winding thereof, thereby to decrease Ithe series resistance of the previously traced circuit for energizing the upper winding of the cutoff relay R6l0, whereupon the latter relay is operated. Upon operating, the cutoff relay R6|0 completes, at the contacts 6i3, a holding circuit for energizing the lower winding thereof, this circuit extending kfrom ground by way'1 of the contacts 645 and 6|3 land the lower winding of R6|0 to battery. Further the cutoff relay R6|0 completes, at the contacts 6|2, a multiple point in the previously traced circuit for energizing the upper winding thereof, interrupts, at the contacts 6|4, 35 the initial path for 'applying battery potential -to the control conductor C683 of the trunk 680 and interrupts, at the contacts 6||, the previously mentioned path for causing ring-back tone current to be returned over the trunk 660, the local finder-selector link 940 andthe telephone line 935 to the calling subscriber substation T4, thereby to indicate to the subscriber thereat that the call has been answered at the switchboard in the P. A. B. X 30. Finally, the cutoff relay R6|0 interrupts, at the contacts 6| 5, the previously traced multiple circuits for illuminating the group line supervisory lamps L|049, LII49, etc., at the various operator positions at the switchboard in order to indicate to the operators thereat that the call on the trunk in the group of trunks, including the trunkV 610, has been 'answered at one of the operator positions at the switchboard.

Further the switching relay R130 completes, at the contacts 138, a holding circuit for energizing the lower winding of the vstart relay R155, this circuit extending from ground by way of the contacts 138 and 159, the lower winding of R155 and the resistor 121 to battery. Finally the switching relay R130 completes, at the contacts 13| and 132, an operative-connection between the position equipment at the rst voperator position 900 and the repeater 660 in the trunk circuit 600, thereby operatively to connect therst operator position 900 at .the switchboard'to the calling subscriber substation T4. More particularly, the position equipment at the first operator position 900 is connected by way of the line conductors C102 and C104 in the cable 60|, the contacts 112 and 115 and the contacts 13| and 132 to the line wipers 1|| `and A1|2 of the switching mechanism 1|0. Further thisl connection extends from the line wiper 1| of the switching mechanism 1 |0 by way of the line conductor C61! of the trunk 610,

the winding 663 of the repeater 660, the contacts 642 and 644, the winding 664 of the repeater 660 and the line conductor C612 of the trunk 610 to the line wiper 1|2 of the switching mechanism 1 I0. Also the windings 663, 664 and the windings 66|, 662 of the repeater 660 are inductively coupled, the windings 66| and 662 of the re' peater 660 being included in the previously traced loop circuit extending from the repeater 660 by way of the trunk 660, the local finder-selector link 940 and the telephone line 935 -to'the calling subscriber substation T4. Hence, atthis time, an operative connection is completed between the calling subscriber substation T4 and the first operator position 300'is advised concerning the extension of the call, and then extends the call in a manner more fully explained hereinafter.

After the operator at the ilrst operator position 900 answers the call she returns the groupline key KI |55 back to its normal position, thereby to interrupt, at the contacts ||51 thereof, the previously-mentioned path for applying ground ypctentialto the f marking conductor C|016 'in the cable |030 in order to remove the marking from the corresponding'contacts in the vertical control contact banks in the-switching mechanisms of the finders of the switching links. Also, at the contacts H56 ofthe group line key KI |55, the previously mentioned path for applying ground potential to the start conductor C|016 in the cable |09| is interrupted, thereby to interrupt the previously traced circuit for energizing the upper winding of the start relay R155, thelatter relay remaining in its'operated position at this time due to the completed holding circuit for energizing the lower winding thereof.

In view of the foregoing explanation of the mode of operation of the nder of the switching link 800 in the group of switching links associated with the first operatorposition 900 to seize the trunk 610, it will be understood that the finder 903 of the switching link 602 in this group of switching links is operative in a similar manner to ind the trunk 610. In other words, the operator at the rst operator position 900 may answer the call on the trunk 610 by utilizing any one of the switching links in the associated group of switching links merely by operating the link key of the finder o f the selected switching link in combination with the group line key K||55, in.

the manner previously explained.

After the operator at the rst operator position 900 answers the call on the trunk 610' and receives the information lconcerning the extension of the call she operates the keysender apparatus -in the position equipment at the first operator position 900, thereby to control the operation of the selector of the selected switching link. More particularly, assuming that the call on the trunk 610 is answered at the first operator position 900 by utilizing the switching link 600, the selector 820 is controlled in order to seize one of the trunks accessible thereto, after which the call is extended by way of the seized trunk to its destination. After extending the call to its destination the operator at the rst operator position 000 returns the talk key K of the finder venergizing the lower winding ofthe connect relay R110 and to interrupt. at the contacts 162, and 131, the previously traced connections between the various conductors in the cable 60| and the various conductors extending by way of the nder 100 and the trunk 82| tothe selector 626. The connect relay R110 then restores to interrupt, at the contacts 11|, 114 and 112, 115, the previously traced connections between the ilnder 100 and the selector 020 and the position equipment at the ilrst operator position 300. Also the connect relay R110 completes, at the contacts 113 and 116, a direct connection between the, finder 100 and the selector 020, thereby to complete an established connection, including the calling subscriber substation T4, the telephone line 035, the local lnder-selector link 640, .the trunk 680, the trunk circuit 600, the trunk 610 and the switching link 800 independent of the' tlrst operator position 300. Further the connect relay R110 completes, at the contacts 11|', an obvious multiple circuity for illuminating the supervisory lamp L125 and interrupts, at the contacts 113', a further point in the previously mentioned path for short-circuiting the lower winding of the start relay R155. Further it is noted that, at the contacts 184 of the talk1 key X180 o! the ilinder of the switching link 800, there is prepared a circuit traced hereinafter for: illuminating the supervisory lamp L126. f

The supervision and release of the established connection, including the switching link 800, is primarily under the control oi the operator at the first operator position 900 and is eiected in the manner explained in the previously mentioned Voss and Crocker patent.

More particularly, when a release operation is performed at the calling subscriber substation T4 the local under-selector link 940 is released and the line circuit 936 is controlled, thereby to mark the telephone line 035 extending to theY subscriber substation T4 as idle to the local connectors having accessthereto. When the localI iinder-selector link 940 is released the previously traced circuit for energizing the upper and lower windings of the line relay R630 in the trunk circuit 600 is interrupted, thereby to cause the latter relay to restore. Upon restoring, the line relay R630 completes, at the contacts 633, a circuit for energizing the lower winding of the recall relay R650, this circuit extending from ground by way of the` contacts624 and 633 and the lower winding of R650 to battery. When thus energized the recall relay R650 operates to complete, at the contacts 65|, a holding circuit for energizing the upper winding thereof and for illuminating the supervisory lamp L126, this circuit extending from ground by way of the contacts 623, the upper winding of R650, the contacts 65|, the control conductor C614 of the trunk 610, the control wiper 1|4 of the switching mechanism 1|0, the conductors C804 `and C8| 3 in the nder 100, the contacts 184 of the talk key K180 of the finder 100 and the supervisory lamp L126 to battery. The illumination of the supervisory lamp L126 indicates to the operator at the ilrst operator position 900 that the established connection routed by way of the switching link 800 has been released. 1

Also the line relay R630 interrupts, at the contacts 632, the previously mentioned circuit for energizing the winding of the hold relay R640, thereby to cause the latter relay to restore shortly thereafter, the hold relay R640 being of the slow-t-release type. Upon restoring, the hold relay R640 interrupts, at the contacts 642 and 644,

the previously mentioned direct connection be-l tween the windings 663 and 664 ot the repeater 660,V completes, atthe contacts 643, an obvious path for applying battery potential by way ofthe resistor 6|6 to the line conductor C612 of the trunk 610 and completes, 'at the contacts 64|, an obvious path for applying ground potential to the line conductor C6'II of the trunk 610, the application oi' ground and battery potentials to the line conductors C61| and C612 of the trunk 610 being utilized for supervisory purposes. Further the hold relay R640 interrupts, at the contacts 645, the previously traced multiple circuit for energizing the winding of the start relay R620 and the lower winding of the cutoil relay R6I0, thereby to cause thestart relay R620 to restore shortly thereafter, the latter relay being of the 'slow-to-release type. However, the cutoi relay R6|6 remains in its operatedposition due to the completed circuit for energizing the upper winding thereof. Upon restoring, the start relay R620 interrupts, at the contacts 62| and 623, the previously mentioned paths for applying battery and ground potentials to the line conductors C612 and C61| of the trunk 610. Also the start relay R620 interrupts, at the contacts 624, the previously traced circuit for energizing the lower winding of the recall relay R650 and interrupts, at the contacts 623, the previously traced holding circuit for energizing the upper winding of the recall relay R650, thereby to cause the recallrelay R650 to restore.

The operator at the rst operator position 900 then operates the talk key K180 of the finder away from its normal position, thereby to cause reoperation of the connect relay R in the finder 100, in the manner previously explained. Upon reoperating, the connect relay R110 again connects the position equipment at the first operator position 900 to the switching link 800, thereby to enable the operator at the ilrst operator position 300 to release the switching link 800.

In order to release the switching link 800 the operator at the first operator position 900 controls the position equipment thereat, thereby to cause ground potential to be applied to the release conductor C108 in the cable 30|. This application of ground potential to the release conductor C108 in the cable 80| completes a path for short-circuiting the lower winding of the start relay R155, this path extending from the grounded release conductor C108 in the cable 90| by way vof the contacts 113', the lower winding of R and the contacts 159 and 138 to ground. When the lower winding of the start relay R155 is thus short-circuited the latter relay restores.

At this point it is noted that, when the wiper set of the switching mechanism 'H0 of the nder 100 is driven one step in the vertical direction, the sets of switch springs S123 and S124 are respectively actuated into engagement and disengagement. When the set of switch springs S123 is actuated into engagement a circuit traced hereinafter is prepared for energizing the release magnet M122; and when the set of switch springs and the release magnet M122 to battery. When thus energized the release magnet` M122 operates to release the wiper set of the switching mechanism 1|0, whereupon the wiper set of the switching mechanism 1|0 is returned to its normal position. Also upon restoring, the start relay R155 interrupts, at the contacts 151, the previously traced holding circuit for energizing the upper winding of the transfer relay R140 and the previously traced holding circuit for energizing the intermediate switching relay R130, thereby to cause the latter relays to restore. When the wiper set of the switching mechanism 4110 is returned -to its normal position the sets of switch springs S123 and S124 are respectively actuated` into disengagement and engagement. When the set of switch springs S123 is actuated into disengagement the previously traced circuit for energizing the release magnet M122 is interrupted, thereby to cause the release magnet M122 to restore. Finally, the start relay R155 interrupts, at the contacts 158, the previously traced original circuit for illuminating the supervisory lamp L125, thereby to cause the supervisory lamp L125 to be extinguished when the selector 820 is released in order to indicate that the switching link 800 is idle at this time. Also, the release of the selector 820 is under the control of the operator at the iirst operator position 900, and is eiected in the manner explained in the previously mentioned Voss and Crocker patent. When the selector 820 is released the previously mentioned alternative circuit for illuminating the supervisory lamp L125 is interrupted, as previously explained.

The operator at the first operator position 900 then returns the talk key K180 of the finder 100 of the switching link 800 back to its normal position, thereby to interrupt, at the contacts 186 thereof, the previously traced holding circuit for energizing the lower winding of the connect relay R110, whereupon the latter relay restores. At this time, both the finder 100 and the selector 820 of the switching link 800 are completely released and the switching link 800 is available for further use.

When the finder 100 of the switching link 600 is released the previously traced circuit for energizing the upper winding of the cutoi relay R6|0 in the trunk circuit 600 is interrupted, thereby to cause the latter relay to restore. Upon restoring, the cutoi relay R6|0 recompletes, at the contacts 6| 4, the previously mentioned path for. applying battery potential by way of the resistor 6|1 to the control conductor C683 of the trunk 680 in order to mark the trunk 680 as idle to the local finder-selector links having access thereto.

At this time, the apparatus utilized in the established connection between the calling subscriber substation T4 and the first operator position 900 at the switchboard is completely released and available for further use.

Similarly, it will be understood that an operator at any other operator position at the switchboard in the P. A. B. X 30 may answer the call on the trunk 610. For example, the operator at the last operator position 9|0 may answer the call on the trunk 610 by operating the group line key K|055 away from its normal position after selecting one of the switching links in the associated group. More particularly, when the operable I 090, thereby to complete a path substantially identical to that previously traced for marking the vertical level in the contact banks of the switching mechanisms of the nders of the.

l of the position equipment at the last operator position 9|0 and the start conductor, not shown, in the cable 9|| into the iinder of the selected switching link, thereby to cause operation of the iinder of the selected switching link, in the manner previously explained, whereupon an operative connection is completed between the calling subscriber substation T4 and the last operator position 9|0. After the call is answered at the last operator position 9|0 the operator thereat returns the group line key K|055 to its normal position, thereby to interrupt, at the contacts |051 and |056, respectively, the previously mentioned paths for applying ground potential to the marking conductor C|016 in the cable |090 and to the start conductor C|01.0 in the cable |092, for the purpose previously'explained. After the operator at the last operator position 9|0 answers the call on the trunk 610 she is advised concerning the extension of the call and then operates the position equipment at the last operator position 9|0 in order to cause the call to be extended in the manner previously explained. The extension, supervision and release of the connection at the last operator position 9|0 are the same as that previously explained in connection with the first operator position 900.

Call from the central olce to the P. A. B. X

In order to extend a call from the central office 20 to the switchboard in the P. A. B. X 30, the operator at the operator position 240 in the central oilice 20 first selects an idle trunk line in the group of trunk lines extending from the central oflce 20 to the P. A. B. X 30, such as the trunk line 205, and then operates the apparatus at the operator position 240, thereby to cause ringing current to be projected over the trunk line 205. The projection of ringing current over the trunk line 205 completes a circuit for energizing the upper winding of the ring-up relay R3|0 in the incoming trunk line circuit 300, this circuit extending from the line conductor C206 of the trunk line 205 by way of the contacts 33|, the condenser 343, the contacts 3|| and the upper winding of R3 |0 to the line conductor C201 of the trunk line 205, the line conductors C206 and C201 of the trunk line 205 having ringing voltage impressed therebetween. When thus energized the ring-up relay R3I0 operates to complete, at the contacts 3|2, a holding circuit for energizing in series the lowerwinding thereof and the lower winding of the start relay R320,

. this circuit extending from ground by way of the tor at the last operator position 9|0 operates the group line key K|055 away from its normal position there is completed, at the contacts |051 thereof, an obvious path for applying ground potential to the marking conductor C|016 in the calower winding of R3l0, the contacts 3|2 and 335 and the lower winding of R320 to battery. When this holding circuit is completed the ring-up relay R3|0 remains in its operated position while the start relay R320 operates. Also the ring-up relay R3|0 interrupts, at the contacts 3| the previously traced original circuit for energizing the upper winding thereof. Upon operating, the start relay R320 completes, at the contacts 323, a path This application of ground potential v,

for .applying battery potential by way of the upper winding thereof to the control conductor C353 of the `trunk 350, thereby to mark the rotary position of the trunk 350 in the main contact banks of the switching mechanisms of the finders of the switching links having access thereto.

Further the start relay R320 completes, at the contacts 324,.an obvious path for applying ground potential to the control conductor C356 in the cable |030, thereby to complete obvious multiple circuits for illuminating the group line supervisory lamps L|048, L||40, etc., at the`various operator positions at the switchboard in order to indicate to the operators thereat that there is an incoming call from the central ofilce to the P. A. B. X on one of the trunks in the group of trunks, including the trunk 350i.

This call may be answered at any oney of the operator positions at the switchboard. For example, in order to answer the -call on the trunk 350 at the first operator position 900, the operator thereat operates the group line key Kl away from its normal position, thereby to complete, at the contacts ||5| thereof, the previously traced path for applying ground potential tothe start conductor C|018 in the cable |0l9| extending to the rlrst operator position 000 in order to initiate operation of the nder of the previously selected switching link in the associated group of switching links. Also, at the contacts |52 of the group line key K||50, there is completed an obvious path for applying ground potential to the marking conductor C|013 in the cable |030, thereby to mark the Vertical level in the vertical control contact banks of the switching mechanisms of the finders of the switching links, wherein the trunk 350 extending to the incoming trunk line circuit 300 is terminated.

The operation of the finder of the selected switching link in the group of switching links associated with the first operator position 900 to seize the trunk 350 is substantially the same as that previously explained; and after the trunk 350 is seized by the finder of the selected switching link the group line key KI |50 is returned to its normal position, thereby to interrupt, at the contacts ||5| and ||52 thereof, the previously traced path for applying ground potential respectively to the start conductor C|018 in the cable |09| and to the marking conductor C|013 in the cable |050.

When the nder of the selected link associated with the first operator position 900 seizes the trunk 350 ground potential is applied to the control conductor C353 thereof, thereby to complete an obvious holding circuit for energizing the upper winding of the start relay R320 and to complete an obvious circuit for energizing the winding of the cutoff relay R330. When thus energized the cutoff relay R330 operates to complete, at the contacts 333, an obvious holding circuit for energizing the winding thereof and to interrupt, at the contacts 335, the previously traced holding circuit for energizing the lower winding of the ring-up relay R3|0 in series with the lower winding of the start relay R320, thereby to cause the ring-up relay R3|0 to restore, ringing voltage being impressed between the line conductors C206 and C201 of the trunk line 205 only momentarily by the operation of the apparatus at the operator position 240 in the central oilice 20. Also the cutoff relay R330 interrupts, at the contacts 336, the previously mentioned path for applying ground potential to the control conductor C356 in the cable |090, thereby to inter- CII rupt the previously traced multiple circuits for illuminating the group line supervisory lamps L|048, L| |43, etc., at the various operator positions atthe switchboard in order to indicate to the operators thereat that the call on the trunk in the group of trunks, including the trunk 350, has been answered at one of the operator positions at the switchboard. Finally the cutoff relay R330 completes, at the contacts 332, an operative connection between the operator position 240 in the central oilice 20 and the repeater 340 in theincoming trunk line circuit 300, this connection extending from the line conductor C206 of the trunk line 205 by way of the contacts 332, the windings 34| of the repeater 340 and the contacts 322 to the line conductor C201 ofthe trunk line 205, the line conductors C206 and C201 of the trunk line 205 being operatively connected to the operator position 240 in the central oilice 20. Also it is noted that the windings 34| and 342 of the repeater 340 are induotively coupled, thereby to establish a connection between the trunk line 205 extending from the operator position 240 in the central oiiice 20 to the incoming trunk line circuit 300 and the trunk` 350 seized by the finder of the switching link operatively associated with the first operator position 900.

The subsequent extension and supervision of the connection at the rst operator position 903 arethe same as that previously explained. The release of the established connection is initiated by the operator at the operator position 240 in the central oilice 20 and is accomplished when the operator at the operator position 240 operates the apparatus thereat, thereby to cause ring-off current to be projected over the trunk line 205. The projection of ring-off current over the line conductor C205 completes an alternative circuit for energizing the upper winding of the ring-up relay R3|0, this circuit extending from the line conductor C206 of the trunk line 205 by way of the contacts 32|, the condenser 343, the contacts 3|| and the upper winding of R3|0 to the line conductor C201 of the trunk line 205, the line conductors C206 and C201 of the Itrunk line 205 having ring-off potential impressed therebetween at the operator position 240 in the central oflice 20. When thus energized the ring-up relay R3|0 operates to complete, at the contacts 3|2, a holding circuit for energizing the lower winding thereof in series with the supervisory lamp L121, this circuit extending from ground by way of the winding of R3|0, the contacts 3|2 and 334, the control conductor C355 vof the trunk 350, the control wiper 1 |4 of the switching mechanism 1|0 of the ilnder 100, the conductors C804 and C8|3 of the nder 100, the contacts 104 of the talk key K180 and the supervisory lamp L126 to battery. The operator at the operator position 240 in the central oflice 20 then operates the apparatus thereat, thereby to interrupt the projection of ring-off current over the trunk line 205 in order further to interrupt the previously traced circuit for energizing the upper winding of the ring-up relay R3|0. The illumination of the supervisory lamp L126 indicates to the operator at the first operator position 900 that the established Vctnnection routed by way of the switching link 800 has been released, whereupon the operator at the rst operator position 900 effects the release of the switching link 800, in the manner previously explained.

When the switching mechanism 1|0 in the nder of the switching link 800 is released the previously traced multiple holding circuit for energizing the upper winding of the start relay R320 and the winding of the cut-oli relay R330 is interrupted, thereby to cause the start relay R320 to restore immediately and to cause the cuto relay R330 to restore shortly thereafter, the cutoff relay R330 being ofthe slow-to-release type. Also when the switching mechanism 1|0 in thevnder 100 of the switching link 800 is released the previously traced holding circuit for P. A. B. X 30 may answer the call on the tru-nk 350. For example, the operator at the last operator position 9 l0 may answer the call on the trunk 350 by operating the group line key Kl050 in combination with the talk key of the iinder of one of the switching links in the group of switching links individually associated with the last operator position 9|0. More particularly, the

R320, this 4circuit extending from ground by way of the contacts 44| and 433 and the winding of R420 to battery. When thus energized the start relayvR420 operates'to complete, at the'contacts 423, an obvious path for applying groundA potential to the control conductor C464 of the trunk 460, thereby to mark the trunk 460 as -busy to the selectors of the'switching links having access thereto. Also the start relay. R420 completes, at the contacts 424 and 425, obvious paths for applying ground potential to the control conductors C461 and-C468, respectively, in the cable |090. The application of ground potential to th'e control conductor C461 in the cable |090 completes obvious circuits for illuminating` the individual line busy lamps L|046, LI |46, etc.. at the various operator positions at the switchboard in the P. A, B. X30, thereby to indicate to the operatorsthereat that the trunk line 2|0 extending between the P. A. B.` X and the I. B. X 40 is :busy at this time. The application of ground p potential to the control conductor C468 in the cable |090 completes obvious circuits for illuminating the individual line answer lamps LI041, LI |41, etc., at the various operator positions at the switchboard in the P. A. B, X 30, thereby to indicate to the operator thereat that there is a call waiting to be answered on the trunk 460 group line key Kl050 is operated away from its normal position, thereby to complete, at the con-- tacts |052 thereof, an obvious path for`appl'ying ground potential to the marking conductor C|013 in the cable |090 in order to mark thel vertical' level in the contact banks of the switching mechanisms of the finders of the switching links, wherein the trunk 350 is terminated. Also,

at the contacts |05| of the group line key Kl050, there is completed an obvious path for applying ground potential to the start conductor C|010 in the cable |092 extending to the last operatorA position 9|0, thereby to initiate operationof the operatively associated, by the trunk line circuit 400, with the trunk line 2|0.

The call on theftrunk 460 may be answered at any one of the operator positions at the switchboard in the P. A. B. x ao.- For exampie, in order to answer the call on the trunk 460 at the nder. of the selected switching link in the group of switching links individually associated with the last operator position 9I0. fThe subsequent operation of the apparatus at the-last operator:

position 9|0 to answer, to extend and to super-E vise the established connection, and the subsequent release of the established connection areY the same as that previously explained.

Call from the I. B. X to the P. A. B. X

In order to extend a call from the I. B. X 40 to the switchboard in the P. A. B. X 30, the

operator at the operator position 260 in the I. B. X 40 rst selects an idle trunk line in the group of trunk lines extending between the I. B'. X 40 and the P. A, B, X 30, such as the trunk line 2|0, and then establishes a connection thereto.. When a connection is established at theoperator position 260 to the trunk line '2|0, a circuit is rst operator position 900, the operator thereat operates the individual line keyl KI |65 in combination with the Atalk key of the nder of a selected one of the switching links in the group of switching links individually associated with the rst operator position 900. Assuming that the switching link 800 is selected at this time, the talk key X180 of the finder 100 ofthe switching link 800 is operated away from its normal position, inthe manner previously explained.

When the individual line -key K||65 is Voperated away from its normal position, there is completed at the contacts `I |61 thereof an obvious path for applying battery potential by way of the resistor H22 to the marking conductor C|080 in' the cable |030, therebyA to mark the rotary position of the contact sets in the contact banks of the switching mechanisms of the completed for energizing in series the upper and lower windings of theV line relay R440 in the trunk circuit 400, .this circuit extending from ground by way of the upper winding of R440 and the winding 45| of the repeater 450 to the line conductor C2|| of the trunk line 2|0; and from battery by way of the lower winding of R440 and the winding 452 of the repeater 450 to the line conductor C2|2 of the trunk line 2I0, the line conductors C2|| and C2|2 of the trunk line 2 I0 being connected together'at the operator position 260 in the I. B. X 40.

"When thus energized the line relay R440 operates to complete, at the contacts 44|, a circuit for energizing the winding of the start relay switching links individually associated with the rst operator position A900, wherein the trunk 460 is terminated.' Also, at the contacts H66 of the individual line key KI |65, there is completed an obvious circuit for energizing in series the winding of the line marking relay R||10 and the upper winding of the lockout relay RI |25. When thus energized, the Vlockout relay RI |25 and the line marking relay RI |10 operate. Upon operating, the lockout relay Rl |25 lcompletes at the contacts H26 an obvious holding circuit for energizing in series the lower winding thereof and the winding of the linemarking relay RI |10, wherebyr both the upper and lower windings of the lockout 'relay R||25 are energized in multiple series relationship with respect to the winding of the line marking relay Rl |10. Also. upon operating, the lockout relay Rl|25 completes at the contacts H29 an obvious path for applying ground potential to the start conductor C|018 in the cable |09| extending to the 

